Inventors of the present invention extensively study for developing a helmet (Patent Literature 1: WO 2005/090049). As a material of a helmet, a polycarbonate resin or the like is widely used from the viewpoint of having high mechanical strength and high heat resistance. A helmet added with a face protection shield made of a polycarbonate resin is also widely known (Patent Literature 2: JP 2003-049316 A). Without being limited to a helmet, the polycarbonate resin is widely used as a material for other components from the viewpoint of its excellent transparency, impact resistance, heat resistance, and easy processability.
By performing an anti-fog treatment process for applying a coating, an anti-fog film laminate or the like onto a surface of a polycarbonate resin prepared as a product, a molded body of a polycarbonate resin is provided. By having such means, it is prepared to withstand for a general use. Also in the field of the inventors' interest, such means can be used for a helmet, a face protection shield of a helmet, a sports goggle, or eyeglasses.
The anti-fog treatment includes a method of preventing fogginess with a water film, which is formed by coating with a surfactant or hydrophilization of a surface layer and a method of using a water-absorbing water-absorption layer for preventing fogginess using a water absorption layer, which is formed on a surface layer. When it is used under conditions not always having high humidity such as a face protection shield of a helmet or a sports goggle, the anti-fog treatment based on a water-absorbing water-absorption layer is used. It has been noted that the polycarbonate resin substrate obtained by the anti-fog treatment based on a water-absorbing water-absorption layer has white turbidity and peeling of a layer with anti-fog treatment, due to low chemical resistance as a property of a polycarbonate resin (Patent Literature 3: JP 2007-210138 A). Due to the intrinsically low chemical resistance of a polycarbonate substrate, when a water-absorbing water-absorption layer is adopted in the presence of water, the polycarbonate substrate is in a state which is likely to have a problem. Sometimes, there may be a breakage. Thus, it leads to the conclusion that preparing a material with chemical resistance by performing a surface treatment of the polycarbonate resin is not feasible. With regard to a means for solving this problem, it is found that the basic solution cannot be provided without altering the properties of a polycarbonate resin to properties of a resin with chemical resistance.
The polycarbonate is usually considered as a favorable resin. Studies have been made to improve the properties of a polycarbonate resin based on it. As one method, it has been tried to perform polymer alloying by using a polycarbonate resin and other resin to improve the properties of a polycarbonate resin. However, with regard to the problem of low chemical resistance of a polycarbonate resin, obtaining newly a resin composition with chemical resistance by performing polymer alloying and modifying helmet materials by using it have not been tried until now.
Based on the technical background described above, problems of a polycarbonate resin which are not necessarily known are examined and the determination is made to obtain, by polymer alloying, a novel resin composition having chemical resistance by improving the low chemical resistance, which is considered as a problem of a polycarbonate resin.
A thermoplastic resin composition consisting of a polycarbonate resin and a polyester resin (as a representative polyester, polyethylene terephthalates are considered) are considered to be a material having both the impact resistance originally owned by a polycarbonate resin and the chemical resistance owned by the polyethylene terephthalates. Further, it is widely used in an automobile, a field of OA, or the like. Although it is expected to solve the problems by using a thermoplastic resin composition consisting of polyethylene terephthalates and a polycarbonate resin that is produced by a specific method, it has not been achieved yet.
According to the resin composition of the related art in which a polycarbonate resin and a polyester resin are combined, the impact resistance of a polycarbonate resin itself may be significantly lowered and also the chemical resistance of a polyester resin itself may not be sufficiently obtained. Further, since such resin composition is often a non-transparent resin, it is not suitable for a transparent material.
The polycarbonate resin having excellent impact resistance is believed to have poor melt viscosity stability, wet heat fatigue property, and chemical resistance. It is believed that producing a novel resin composition by polymer alloying of polyethylene terephthalates with good chemical resistance and wet heat fatigue property and a polycarbonate resin enables an improvement of the physical properties. However, a resin composition of polyethylene terephthalates using ethylene glycol as an aliphatic glycol shows a significantly lowered hinge properties and lowered wet heat fatigue resistance in repeated bending to yield a case exhibiting breakage of a molded body, which may be due to a progress of crystallization of polyethylene terephthalates and hydrolysis of a polycarbonate resin after exposure to a high temperature and high humidity condition for a long period of time, and as a result, it is believed that no success has been made yet.
For such reasons, it is considered that, in a field requiring mechanical strength, chemical resistance, or a wet heat fatigue property, for example, a material satisfying the requirement for use as an outer handle or an inner door handle as an automobile component, or a mechanical component like a cover of an electric power tool has not been obtained yet. Examination is made regarding the following invention for obtaining a thermoplastic resin composition with excellent melt viscosity stability, wet heat fatigue property, or the like while maintaining the impact resistance and chemical resistance originally owned by the polycarbonate resin and polyalkylene terephthalates.
A suggestion has been made regarding a “thermoplastic resin composition consisting of 5 to 95 parts by weight of polycarbonate (A), in which the main repeat unit is represented by the formula (1) (omitted), and 95 to 5 parts by weight of polyester (BT), in which the main repeat unit is represented by the formula (2) (omitted), and having melt viscosity stability of 2.5% or less (Patent Literature 4: JP 2002-294060 A, Patent Literature 5: JP 2000-143951 A, and JP 3973303 B1).
With regard to a solution for the above problem, when the polycarbonate component is used in a large amount, an influence of the polycarbonate becomes higher, and as a result, it is unavoidable to have a product having undesirable properties of polycarbonate. The polycarbonate as a material used for a helmet or the like is left to have a result of having low chemical resistance, which is an undesirable property of the polycarbonate.
Accordingly, for improving the chemical resistance not owned by a polycarbonate resin, it is considered to stop using a polycarbonate resin as a resin for substrate, but use a resin having chemical resistance as a substrate and perform polymer alloying in combination with other resin.
If the polyester resin is used for a helmet material, there is an improvement in terms of chemical resistance, which is problematic in the polycarbonate resin. However, as it is insufficient in terms of weather resistance and low-temperature impact resistance, improvements are needed therefor. Because the inventors of the present invention knew from experience that, even for a case of using a polyester resin, use of a polyester resin of the relate art is not sufficient in terms of the properties but use of poly(1,4-cyclohexylene dimethylene terephthalate)copolyester (Patent Literature 6: JP 3432830 B1 and JP 11 512484 W) is effective. As such, use of poly(1,4-cyclohexylene dimethylene terephthalate)copolyester resin is taken as a measure for solving the problems.
It is urgently needed to obtain a resin having weather resistance and low-temperature impact resistance, which are regarded as a problem of a poly(1,4-cyclohexylene dimethylene terephthalate) copolyester resin, by performing polymer alloying using a resin composition in which a poly(1,4-cyclohexylene dimethylene terephthalate) copolyester resin is combined with other resin, and also to obtain a resin composition maintaining the chemical resistance and impact resistance at room temperature that are originally owned by the poly(1,4-cyclohexylene dimethylene terephthalate) copolyester resin.
In Patent Literature 7, a molded body having 5 to 95% by weight of a polyester consisting of a terephthalic acid residue, a 2,2,4,4-tetramethyl-1,3-cyclobutane diol residue, and a cyclohexane dimethanol residue and 5 to 95% by weight of polycarbonate is suggested. However, the molded body does not have an improvement in low-temperature impact resistance. Further, there is no improvement of chemical resistance depending on the nature of the composition. Still further, there is no improvement of weather resistance.